1. Field of the Invention
The present invention relates to an image heating apparatus effectively used as a fixing device in an image forming apparatus such as a copier or printer. In particular, the present invention relates to an image heating apparatus of an induction heating type.
2. Description of the Related Art
The following describes by way of example a heating apparatus (image heat-fixing apparatus) for fixing an unfixed toner image formed on a recording material in an image forming apparatus such as an electrophotographic apparatus or electrostatic recording apparatus. Conventionally, contact heating systems such as hot roller and film heating types have been widely used in heating apparatuses for fixing unfixed toner images. A heating apparatus using an electromagnetic induction system as its heating source is proposed lately.
A heating apparatus for an unfixed full-color image might be required to superimpose toner layers on top of one another up to a four-ply layer. Since the unfixed full-color image needs to be heated sufficiently into the interface surface between a recording material and the toner layers so as to prevent occurrence of a fixing failure, the overlapped toner layers must be held firmly until all the toner layers are fixed.
A control method for the electromagnetic induction type heating apparatus is proposed in Japanese Patent Laid-Open Application No. 10-171296. The publication proposes that preliminary rotation and preliminary heating of a fixing film be performed during the time the apparatus is on standby in such a structure that the fixing film of small heat capacity as an electromagnetic induction heating type rotary body itself locally generates heat, thereby reducing first printing time (FPT).
Such a control method as to perform preliminary rotation and preliminary heating of the fixing film during the time the apparatus is on standby, however, increases the number of rotations of the fixing film in a case where the printer is infrequently used and hence its standby state lasts a long time. As a result, the rotating ratio of the fixing film during a standby period to the endurance of the heating apparatus becomes high to reduce the number of printable sheets.
The present invention has been made in consideration of the above-mentioned conventional problems, and it is an object thereof to provide an image heating apparatus capable of preventing occurrence of a fixing failure.
It is another object of the present invention to provide a long-lifespan image heating apparatus.
It is still another object of the present invention to provide an image heating apparatus comprising:
a rotation member;
an excitation coil for generating a magnetic field to induce an eddy current in the rotation member;
a temperature detecting element for detecting a temperature of the rotation member; and
control means for controlling an electrical supply to the excitation coil so that the temperature detected by the temperature detecting element is maintained at a set temperature,
wherein while the set temperature is set to a standby temperature, the control means controls the electrical supply to the excitation coil and the rotation member is maintained in a stoppage of rotation.
It is yet another object of the present invention to provide an image heating apparatus comprising:
a heating member;
an excitation coil for generating a magnetic field to induce an eddy current in the heating member;
a temperature detecting element for detecting a temperature of the heating member; and
control means for controlling an electrical supply to the excitation coil so that the temperature detected by the temperature detecting element is maintained at a set temperature,
wherein the control means sets the set temperature in accordance with a temperature of the excitation coil during a standby period.
It is yet another object of the present invention to provide an image heating apparatus comprising:
a heating member;
an excitation coil for generating a magnetic field to induce an eddy current in the heating member;
a temperature detecting element for detecting a temperature of the heating member; and
control means for controlling an electrical supply to the excitation coil so that the temperature detected by the temperature detecting element is maintained at a set temperature,
wherein the control means sets the set temperature to a first set temperature when a temperature of the excitation coil is a first temperature, and sets the set temperature to a second temperature lower than the first set temperature when the temperature of the excitation coil is a second temperature higher than the first temperature during a standby period.
Further and other objects of the present invention will become apparent from reading the following detailed description in connection with the accompanying drawings.